Often times a location of a user within a predefined area (e.g. a building) needs to be monitored. For example, the user may be fire personnel within a building and monitoring the fire personnel's location in the building may be necessary. To accurately estimate the user's location in the building, an altitude of the user needs to be calculated. Most existing inertial navigational devices use barometric pressure sensors to aid in the estimation of altitude. One such example is Motorola's Precision Inertial Navigation Systems (PINS) prototype Personal Tracking Device (PTD). In such existing inertial navigational devices, altitude data of the user is recorded at the inertial navigational device and communicated to a remote device where the remote device estimates the location of the user.
Because altitude data is recorded at the inertial navigational device, as barometric conditions change or shift (for example as a cold front moves through), existing navigational devices cannot compensate for local pressure changes and can confuse local pressure changes with changes in the altitude of the inertial navigational device. Not compensating for local pressure changes causes errors in estimating altitude of the inertial navigational device. Not being able to accurately estimate altitude of the inertial navigational device means that the location of the user (e.g. fire personnel) is mistaken.
Thus, there exists a need for a new way to correct altitude of a navigational device.